casting with sand moulds

simple Andrew,
The sand that hardens with CO2 is fine dry silica sand mixed with 3 to 4% by weight sodium silicate (John Winter & Co Halifax) and very thorougly mixed. For normal run of the mill work I use bagged kiln dried sand intended for 'grouting' paving sold by builders merchants, but use fine core sand (expensive) for small scale fine detail , and mix it in a paddle mixer (look up Belle Tubmix) or use a plaster mixing paddle in a drill and bucket if smaller quantities. It is very important to make sure it is fully mixed - very easy to get unmixed pockets that won't set. Don't try mixing with moistened sands - you'll get a very disapointing result. I set mine using a CO2 cylinder and regulator with a simple funnel on the end of a hose. If you want easy breakout for fine details and cores etc mix in about 1% icing sugar (but don't tell the wife). For open moulds for ingots etc I'll go to the high end of the silicate addition, and for delicate stuff err on the low side. The more you use the stronger the bond and the less permiability you get for the gases to pass through.
When sodium silicate (waterglass) reacts with CO2 it forms crystals of solid silica gel which is nice and hard, but of course will absord moisture, so don't leave moulds lying about for weeks unless you bake them before use.
The resin sands are set with a catalyst usually dispensed in correct proportion by the sand blower in a 'proper' foundry.
I've just been out to my foundry to check, and as I suspected, my Sodium Silicate drum is "Winterbond 80" so it ain't resin !!!!!
AWEM

Didn't that hurt?
Peter

A friend of mine showed my his *very* *first* Al-casting that he did with oil-bound sand (I think "petro-bond" is one of the brand-names). It really was incredible. As a pattern, he used a crank case of a radial engine out of a plasic kit (diameter about 100mm, height 50mm, bell-shaped). You even saw the tiny hex-nuts (width about 2mm). Wall-thickness about 1...1.5mm. He only made some errors with the raiser and feeder and venting, so it wasn't completely filled (20% missing).
Nick, not yet into al-casting

no but provides a good talking point I keep it to compare my real hand to just in case I start waisting away andrew

thanks Andrew just what I needed to know I brought a small electric furnace on ebay and just won't to make few small bits first if its as much fun as I remember I may build a bigger gas version or look for a bigger electric one but not on your scale that's scary
andrew